1. Field of the invention
The present invention relates to a generator for generating multiple ramp signals. Such a generator is preferably for generating a xe2x80x98solidxe2x80x99 used in a video wipe generator of a vision mixer.
A solid is an electrical signal representing a three dimensional surface of a desired shape. It comprises at least one ramp signal and typically comprises a combination of at least two ramp signals which themselves may be modified. It may also comprise a signal defined by a polar coordinate system and representing a curved surface.
2. Description of the Prior Art
Reference will now be made to FIGS. 1 to 3 of the accompanying drawings which show background to the present invention.
FIG. 1 illustrates a known simple wipe between two video sources X and Y.
As the wipe proceeds as indicated by arrow W, video X is replaced across the display by video Y (or vice versa). The effect of a wipe is achieved by mixing the video sources X and Y according to
KX+(1xe2x88x92K)Y
where K is a keying signal. The keying signal K is derived from a xe2x80x98solidxe2x80x99. This will be explained with reference to FIGS. 2 and 3 i.e. a function having a value depending on the h and v co-ordinates within the picture, where v represents line number and h represents pixel position along a line.
FIG. 2 a illustrates a known example of a xe2x80x98solidxe2x80x99 which is a simple ramp. As shown in FIG. 2, a clip level CP is defined. It will be appreciated that over a field or frame, the clip level defines a plane referred to herein as the clip plane, which will be described in more detail with reference to FIG. 4 below. The keying signal K is, in known manner, derived from the solid by applying high gain to the solid and limiting the result, as shown in FIG. 2B. The keying signal has two levels 0 and 1. The transition between the levels occurs where the solid intersects the clip plane CP. The position of intersection is varied, to produce the wipe, by adding an offset to the solid.
FIG. 3 is a schematic block diagram of a wipe generator of a vision mixer comprising a solid generator, a clip element, a gain element, a limiter and a mixer which mixes video sources X and Y in dependence upon the keying signal K.
The solid generator produces a solid, for example a ramp as shown in FIG. 2A. The clip element applies an offset to the ramp to vary the intersection of the ramp with the clip plane CP as shown in FIGS. 2A to 2C. Gain is applied to the offset ramp, in the gain element and the result limited in the limiter to produce the signal K. The amount of gain applied may be varied as shown in FIG. 2B: that varies the slope of the transition between the limit values of the keying signal K.
The mixer mixes the video sources X and Y according to
KX+(1xe2x88x92K)Y.
Thus if K=1, the output is X, if K=0 the output is Y.
If the gain applied to the solid is unity and the clip offset is zero, the solid and the keying signal are identical.
The present invention concerns the solid generator.
It is desired to produce multiple ramps. The production of multiple ramps allows multiple identical solids to exist in one video frame, allowing multiple wipes to occur in a frame.
According to one aspect of the present invention, there is provided a solid generator comprising:
a ramp generator for producing a ramp signal R
R=Ah+Bv+C
where the coefficients
A, B and C are signed values,
the ramp signal R being produced for each pixel of a predetermined set of pixels h where h=0 to n of each of a predetermined set of lines v where v=O to m;
a coefficient generator for generating the values of the coefficients A, B and C; and
control means for causing the ramp signal to be generated with the same values of A and B in each of a plurality of contiguous areas of a picture.
The term xe2x80x9cpicturexe2x80x9d used herein and in the claims is generic to a xe2x80x98fieldxe2x80x99 and to a xe2x80x98framexe2x80x99.
By providing a ramp generator and controlling it to produce a ramp repeatedly in each of a plurality of contiguous areas (referred to as xe2x80x98tilesxe2x80x99 in the following illustrative description) it is possible to create a plurality of identical solids (each of which maybe a single ramp) in the area.
According to another aspect of the present invention, there is provided a solid generator comprising
a plurality P of ramp generators each for producing a ramp signal
Rp=Aph+Bpv+Cp
where p=1 to P
where the coefficients Ap, Bp and Cp are signed values, the ramp signal Rp being produced for each pixel of a predetermined set of pixels h where h=o to n of each of a predetermined set of lines v where v=o to m;
means for generating coefficients Ap, Bp and Cp for the ramp generators;
control means for causing each ramp signal Rp to be generated with its same values Ap and Bp in each of a plurality of contiguous areas of a picture; and
means for combining the ramp signals.
By providing a plurality of ramp generators and controlling them to produce respective different ramps repeatedly in each of a plurality of contiguous tiles it is possible to create identical complex solids in the tiles.
In an embodiment of the invention boundary signals are produced indicating the boundaries of the tiles. By offsetting the boundary signals xe2x80x98partialxe2x80x99 tiles may be produced along e.g. a horizontal and/or vertical edge of the picture. The ramps are correspondingly offset in the xe2x80x98partialxe2x80x99 edge tiles so that the solid displayed in the part tile is identical to the solid in the corresponding part of an adjacent whole tile.
A row of tiles may be offset relative to an adjacent row of tiles by appropriate offsetting of the boundary signals and the ramps.
By continually varying the offsets, tiles may be made to pan across or up/down the picture.
A preferred embodiment of the ramp generator comprises:
means for storing the coefficients Ap, Bp, and Cp and first and second accumulated values,
adding means for incrementing the first accumulated value by Ap and the second accumulated value by Bp, and
control means by which , for each of the said lines v, the second accumulated value is incremented by the adding means by Bp to form Cp+Bpv which is stored as both the first and the second accumulated values, and for each pixel of the said set of pixels on each of the said lines the first accumulated value is incremented by the adding means to form
Cp+Bpv+Aph
which is stored as the first accumulated value and is output as Rp.
The storing means which are preferably registers allow the coefficients A, B and C to be easily changed for the purposes of generating different ramps.
By varying the content of the register storing Cp the offsetting mentioned above can be achieved.
The ramp generator does not require the use of multipliers.